The rates of synthesis of the polyamines (spermidine and spermine) and their metabolic precursor putrescine are elevated during the proliferative response of mammalian cells. The cellular levels of two key enzymes of polyamine biosynthesis, ornithine decarboxylase and S-adenosylmethionine decarboxylase, are greatly elevated early in the response of small lymphocytes to mitogenic activation. Initially, the studies proposed here will concentrate regulation of S-adenosylmethionine decarboxylase. The enzyme has been purified and rabbit antiserum and mouse monoclonal antibodies have been prepared to it. We have measured the rate of synthesis in intact lymphocytes and it is stimulated 10-fold within 9 hrs after mitogenic activation. cDNA clones coding for S-adenosylmethionine decarboxylase will be prepared for studying the regulation of its rate of synthesis. Two experimental approaches will be taken: (1)\synthetic DNA probes, based on amino acid sequences from the protein, will be used to screen a bovine lymphocyte cDNA library and (2)\monoclonal antibodies will be used to enrich for polysomes specific S-adenosylmethionine decarboxylase and cDNA copies of polyA+RNA isolated from these polysomes will be cloned. After subcloning these cDNAs into the single-stranded bacteriophage fd, these recombinant DNA probes will be used to investigate the mechanism of translational and transcriptional control of this enzyme in mitogen-activated lymphocytes. (J)